1. Field of the Invention
The present invention relates generally to constant temperature devices, and more specifically to the use of chemical energy in such devices to provide a source of heat.
2. Description of the Prior Art
It is often desirable to increase the skin temperature of a person to provide an increase in comfort or blood circulation, or to aid in overcoming the adverse effects of shocks. Blankets have often been used in these situations to inhibit the flow of heat from a person to his environment. This type of blanket has not provided a source of heat, but rather has performed the function of an insulation so that the skin temperature of the person has only been slightly greater than its normal temperature.
To provide even higher skin temperatures, devices such as hot water bottles have been applied directly to the skin of the person to provide a source of heat. Since the effective period of use of the bottle has been directly related to the initial temperature of the water therein, these hot water bottles have either been initially uncomfortably hot, or their period of effective use has been relatively short. Furthermore, the temperature of the bottle has not remained constant over the effective period of its use so that initially it has been too hot and ultimately it has been too cold.
Heating pads and blankets including electrically energized coils have also been used to provide a source of heat. Typically, the coils have been energized through a thermostat, and delays inherent in the response of the device to the operation of the thermostat have caused significant fluctuations about a desired temperature.
Another type of heat source is a hydrocollator which is commonly used in physical therapy to provide a patient with a source of moist heat for an extended period of time. The hydrocollators of the prior art include canvas bags which are filled with sand and heated in boiling water. When the bag is sufficiently hot it is typically wrapped in a wet towel before application to the patient. Although these hydrocollators have been reusable, they have not provided a source of substantially constant temperature heat.
Other localized sources of heat have included a first container enclosing a first chemical such as calcium chloride. A second rupturable container has been disposed interiorly of the first container and has enclosed a second chemical having characteristics for exothemically reacting with the first chemical. These devices of the prior art have been particularly effective in providing a heat source of substantially constant temperature. Also, these devices have provided means for initiating the exothermic reaction by merely striking the first container to rupture the second container. Although these chemical devices of the prior art have been effective with respect to the hot water bottles and heating pads, it is always desirable to provide a constant temperature device which can be recycled to provide a source of heat at a subsequent controllable time.